She added: "I think there's a reason for changing the rules, but not for introducing a new allowance, which would enhance the position of incumbents."

Liberal Democrat spokesman David Heath said: "We have to be extremely careful when we are seen by those outside to be awarding ourselves yet another allowance of substantial size, without a clear indication of how the money spent is to the advantage of our constituents rather than us."

'No campaigning'

The existing allowance can be used for constituency news letters, press releases, petitions, contact cards and online surgeries.

It cannot be used for fundraising, campaigning, business activities, encouraging people to join a political party, or for petitions or surveys associated with national or local elections.

The £10,000 limit for the new allowance was set by the Members Estimate Committee after MPs agreed there should be money "to assist in the work of communication with the public on parliamentary business".

The committee said MPs had been told they needed to do more to communicate with the public, and that "the traditional method of communicating by letter has shown no sign of abating".

It estimated that the total annual cost of the communications allowance would be about £6m, while the pre-paid envelope allowance would be limited to £4m.

Last year, House of Commons figures showed that MPs claimed almost £86.8m in expenses and allowances - an increase of nearly £6m on the previous year.

The 2005/06 payments - about £131,000 per MP - come on top of a basic salary of about £60,000 and a pension.